The present invention relates generally to voltage reference generation circuits, and more specifically to the generation of voltages related to transistor threshold voltages.
Metal oxide semiconductor (MOS) transistors have a xe2x80x9cthreshold voltagexe2x80x9d (Vt) that can change as a result of process and temperature variations. Process variations occur during manufacture of the MOS transistor, and temperature variations occur as the MOS transistor is operating.
When the voltage across two terminals of the MOS transistor is below the threshold voltage, the MOS transistor is off. When the voltage across the terminals increases to the threshold voltage, the MOS transistor turns on, and begins to conduct current. When the voltage increases much beyond the threshold voltage, the MOS transistor can operate in xe2x80x9csaturation.xe2x80x9d
Some circuits can benefit from receiving a voltage that is equal or nearly equal to a threshold voltage of a MOS transistor. Some circuits can also benefit from receiving a voltage that is a function of the threshold voltage of a MOS transistor. If a fixed voltage is provided to the circuit, problems can arise in part because the threshold voltage of the MOS transistor changes over process and temperature, and the desired relationship between the threshold voltage of the MOS transistor and the received voltage is not maintained.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a method and apparatus that can generate voltages that are related to threshold voltages over process and temperature variations.